JP7455506B2 - Magnetic detection device and moving object detection device - Google Patents

Description

The present invention relates to a magnetic detection device that detects magnetic field changes due to relative movement of a moving object, and a moving object detection device equipped with the same.

2. Description of the Related Art Conventionally, magnetic detection devices have been used to detect the position (rotation detection) of moving bodies such as soft magnetic gears. The magnetic detection device disclosed in Patent Document 1 below applies an alternating magnetic field to a moving body and uses a magnetic sensor to detect changes in the magnetic field due to relative movement of the moving body. According to this, movement detection is possible even if the moving body is a non-magnetic material such as copper or aluminum.

Re-published patent WO2017/073280 publication

The magnetic detection device of Patent Document 1 includes a synchronous detection section that synchronously detects output signals of the magnetic sensor. In synchronous detection, generally, a signal for detection and a signal to be detected are multiplied by a multiplier, and high-frequency components are removed by a low-pass filter. Since the multiplier has a large circuit scale, it has been difficult to reduce the size and cost of the magnetic detection device.

The present invention has been made in recognition of this situation, and an object of the present invention is to provide a magnetic detection device and a moving object detection device that can be made smaller and lower in cost than conventional devices.

An embodiment of the present invention is a magnetic detection device. This magnetic detection device is
A magnetic detection device that detects magnetic field changes due to relative movement of a moving object,
a magnetic field generating conductor;
a voltage application unit that applies an alternating voltage to the magnetic field generating conductor to generate an alternating magnetic field for application to a moving body;
a magnetic sensor having a bridge circuit including at least one magnetoresistive element to which a magnetic field generated by the magnetic field generating conductor and which changes due to relative movement of the moving object is applied;
An alternating voltage output from the voltage application section is applied to the bridge circuit .

The magnetic sensor may include a low-pass filter that passes the output signal of the magnetic sensor.

a differential amplifier into which the output voltage of the magnetic sensor is input;
a negative feedback magnetic field generating conductor that is supplied with current from the differential amplifier and generates a negative feedback magnetic field that brings the magnetic sensor into a magnetically balanced state;
The device may further include current-voltage converting means for converting the current supplied from the differential amplifier to the negative feedback magnetic field generating conductor into a voltage and outputting the voltage to the low-pass filter.

Another aspect of the present invention is a moving object detection device. This moving object detection device is
a magnetic detection device;
A moving body that moves relative to the magnetic detection device,
The magnetic detection device includes:
a magnetic field generating conductor;
a voltage application unit that applies an alternating voltage to the magnetic field generating conductor to generate an alternating magnetic field to be applied to the moving object;
a magnetic sensor having a bridge circuit including at least one magnetoresistive element to which a magnetic field generated by the magnetic field generating conductor and which changes due to relative movement of the moving body is applied;
An alternating voltage output from the voltage application section is applied to the bridge circuit .

The magnetic detection device includes a low-pass filter that passes the output signal of the magnetic sensor,
The moving body has first and second portions having mutually different electrical conductivity or magnetic permeability, or at least one convex portion or concave portion,
The frequency of the alternating voltage outputted by the voltage application section is a frequency equal to or higher than the fluctuation frequency of the electrical conductivity or magnetic permeability of the portion of the moving body that faces the magnetic detection device, or the frequency of the variation between the moving body and the magnetic detection device. The frequency may be higher than the variation frequency of the facing distance.

Note that arbitrary combinations of the above components and expressions of the present invention converted between methods, systems, etc. are also effective as aspects of the present invention.

According to the present invention, it is possible to provide a magnetic detection device and a moving object detection device that are smaller in size and lower in cost than conventional devices.

1 is a schematic perspective view of a moving object detection device 1 according to Embodiment 1 of the present invention. FIG. 2 is a front cross-sectional view of the magnetic detection device 10 of FIG. 1. FIG. FIG. 2 is a plan view of the magnetic detection device 10. FIG. 2 is a diagram (part 1) explaining the detection principle in the moving body detection device 1 when the rotating body 20 to be detected has conductivity. Diagram explaining the detection principle (Part 2). A circuit diagram of the magnetic detection device 10. FIG. 7 is a waveform diagram of the magnetic field H applied to the GMR element bridge circuit of FIG. 6 and the sensor output voltage Vout. 3 is a circuit diagram of a magnetic detection device according to Comparative Example 1. FIG. FIG. 9 is a waveform diagram of the magnetic field H applied to the GMR element bridge circuit of FIG. 8 and the sensor output voltage Vout. FIG. 2 is a schematic perspective view of a moving object detection device 2 according to Embodiment 2 of the present invention. FIG. 3 is a schematic perspective view of a moving object detection device 3 according to Embodiment 3 of the present invention. FIG. 4 is a schematic perspective view of a moving object detection device 4 according to Embodiment 4 of the present invention. FIG. 5 is a schematic perspective view of a moving object detection device 5 according to Embodiment 5 of the present invention. FIG. 6 is a schematic perspective view of a moving object detection device 6 according to a sixth embodiment of the present invention. FIG. 7 is a schematic perspective view of a moving object detection device 7 according to Embodiment 7 of the present invention. The circuit diagram of magnetic detection device 10A in Embodiment 8 of the present invention. FIG. 3 is a circuit diagram of a magnetic detection device according to Comparative Example 2.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the same or equivalent components, members, etc. shown in each drawing are given the same reference numerals, and redundant explanations will be omitted as appropriate. Furthermore, the embodiments are merely illustrative rather than limiting the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

(Embodiment 1)
Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 7. The XYZ axes, which are orthogonal three axes, are defined by FIGS. 2 to 5. As shown in FIG. 1, the moving body detection device 1 of this embodiment includes a magnetic detection device 10 and a rotating body 20 as a moving body. The magnetic detection device 10 is provided at a position facing the outer peripheral surface (outer peripheral portion) of the rotating body 20 on the radially outer side of the rotating body 20, and detects changes in the magnetic field due to rotation of the rotating body 20. The rotating body 20 has a gear shape and has a convex portion 21 as a first portion and a recess portion 22 as a second portion on the outer peripheral surface (outer peripheral portion). In the example of this embodiment, the convex portions 21 and the concave portions 22 are provided on the outer peripheral surface of the rotating body 20 alternately at the same pitch over the entire circumference. The rotating body 20 may be a soft magnetic material or may be electrically conductive (preferably made of metal or a conductor). The detection principle in each case will be described later.

As shown in FIGS. 2 and 3, the magnetic detection device 10 includes a substrate 11, a coil 12 as a magnetic field generating conductor, and a magnetic sensor 13. The coil 12 is provided (fixed) on the substrate 11 and spirals around the magnetic sensor 13 . The axial direction of the coil 12 is preferably perpendicular to the axial direction of the rotating body 20. The coil 12 generates an alternating magnetic field directed toward the rotating body 20 in response to a signal supplied from a signal generating section 18b (FIG. 6), which will be described later. A magnetic field that is generated by the coil 12 and changes as the rotating body 20 rotates is applied to the magnetic sensor 13 .

The magnetic sensor 13 includes a magnetically sensitive element chip 14 and a soft magnetic body 16. The magnetically sensitive element chip 14 is provided (fixed) on the substrate 11, and the soft magnetic material 16 is provided (fixed) on the magnetically sensitive element chip 14. The magnetically sensitive element chip 14 has GMR elements 15a to 15d (GMR: Giant Magneto Resistive effect) as magnetically sensitive elements. As shown in FIG. 3, the GMR elements 15a to 15d are arranged in pairs on both sides in the X direction with the soft magnetic body 16 (the central axis of the coil 12) in between. In FIG. 3, the arrows shown inside each GMR element 15a to 15d are the magnetization directions of the pinned layers (fixed layers) of the GMR elements 15a to 15d, and the pinned layer magnetization directions of the GMR elements 15a to 15d are all in the -X direction. It becomes. As shown in FIG. 6, GMR elements 15a to 15d are full bridge connected. The soft magnetic material 16 is located at the central axis of the coil 12, and strengthens magnetic field components in directions (here, the XY directions at the positions of the GMR elements 15a to 15d) that contribute to the output (resistance change) of the GMR elements 15a to 15d. have a role.

As shown in FIGS. 4 and 5, the distance between the rotating body 20 and the magnetic detection device 10 changes depending on its relative movement. That is, when the convex portion 21 of the rotating body 20 faces the magnetic detection device 10 as shown in FIG. 4, the facing distance between the rotating body 20 and the magnetic detection device 10 becomes smaller (nearer), and When the concave portion 22 of the rotating body 20 faces the magnetic detection device 10, the facing distance between the rotating body 20 and the magnetic detection device 10 increases (becomes far).

4 and 5 show the detection principle when the rotating body 20 has conductivity. As shown in FIG. 4, when the convex portion 21 of the rotating body 20 faces the magnetic detection device 10, a relatively large eddy current is generated in the convex portion 21 located in front of the magnetic detection device 10, and the relative A large demagnetizing field is fed back to the GMR elements 15a to 15d of the magnetic detection device 10, and the sensor output obtained by synchronous detection, which will be described later, becomes relatively small. On the other hand, as shown in FIG. 5, when the recess 22 of the rotating body 20 faces the magnetic detection device 10, a relatively small eddy current is generated in the recess 22 located in front of the magnetic detection device 10. The small demagnetizing field is fed back to the GMR elements 15a to 15d of the magnetic detection device 10, and the sensor output obtained by synchronous detection, which will be described later, becomes relatively large.

Although not shown, when the rotating body 20 is a soft magnetic material, when the convex part 21 of the rotating body 20 faces the magnetic detection device 10, the case where the concave part 22 faces the magnetic detection device 10 is compared to the case where the concave part 22 faces the magnetic detection device 10. , the magnetic field generated by the coil 12 is strengthened (the magnetic field applied to the GMR elements 15a to 15d is strengthened), and the sensor output increases. Regardless of whether the rotating body 20 is a soft magnetic material or conductive, the sensor level differs depending on whether the magnetic detection device 10 is facing the convex portion 21 or the concave portion 22 of the rotating body 20. An output is obtained, and the rotational state such as the rotational speed of the rotating body 20 can be detected. When the rotating body 20 is a soft magnetic material and also has electrical conductivity, the convex portion 21, which is a soft magnetic material, has the effect of relatively increasing the sensor output by strengthening the magnetic field applied to the GMR elements 15a to 15d, and the electrical conductivity. The influence of the convex portion 21 having a magnetic field that relatively reduces the sensor output due to the demagnetizing field coexists, and the larger influence appears strongly in the relative magnitude of the sensor output.

FIG. 6 is a circuit diagram of the magnetic detection device 10. GMR elements 15a to 15d are connected in a full bridge manner to form a GMR element bridge circuit. An interconnection point between the GMR elements 15a and 15b is connected to an output terminal of a signal generation section 18b serving as a voltage application section. An interconnection point between the GMR elements 15a and 15c is connected to an inverting input terminal of a differential amplifier 17 such as an operational amplifier. An interconnection point between GMR elements 15b and 15d is connected to a non-inverting input terminal of differential amplifier 17. An interconnection point between the GMR elements 15c and 15d is connected to ground as a fixed voltage terminal.

The differential amplifier 17 operates in response to power supply voltages Vcc and -Vcc. An output terminal of differential amplifier 17 is connected to an input terminal of low-pass filter 18a. A resistor 19 is connected between the output terminal of the differential amplifier 17 and ground. The resistor 19 is provided to reliably determine the voltage of the output terminal of the differential amplifier 17 with respect to the ground, but may be omitted if unnecessary.

A coil 12 is connected between the output terminal of the signal generating section 18b and the ground. Coil 12 is provided in parallel with the GMR element bridge circuit. The signal generation unit 18b applies an alternating voltage to the coil 12 to generate an alternating magnetic field, and inputs the alternating voltage to the GMR element bridge circuit composed of the GMR elements 15a to 15d (supplies it as an operating voltage). Although not shown, a phase adjusting means is provided to adjust the phase of the alternating voltage output from the signal generating section 18b and inputting it to the GMR element bridge circuit, so that an alternating magnetic field is generated in the coil 12 by the alternating voltage from the signal generating section 18b. (that is, the phase of the resistance value change of the GMR elements 15a to 15d) may be made to match the phase of the voltage applied to the GMR element bridge circuit. The coil 12 may be provided in series with the GMR element bridge circuit. In this case, even without providing the above-mentioned phase adjustment means, the phase of the current flowing through the coil 12 (the phase of the alternating magnetic field generated by the coil 12), the voltage applied to the GMR element bridge circuit, and the voltage flowing through the GMR element bridge circuit can be adjusted. Since the phases of the currents match, there is an advantage that the circuit configuration can be simplified.

The output voltages of the GMR elements 15a to 15d are amplified by the differential amplifier 17 and input to the low pass filter 18a. The low-pass filter 18a removes high frequency components of the output signal of the differential amplifier 17. The voltage at the output terminal of the low-pass filter 18a becomes the sensor output voltage Vout. As will be described later, the sensor output voltage Vout is obtained by synchronously detecting the magnetic field signal applied to the GMR element bridge circuit. An amplifier may be provided to convert the sensor output voltage Vout into a binary value.

The frequency Fs of the alternating voltage output by the signal generation section 18b is determined by the rotational speed of the rotating body 20 and the arrangement pitch of the convex portions 21 or concave portions 22 of the rotating body 20, and the facing distance between the rotating body 20 and the magnetic detection device 10. (Fs≧Fc). Preferably Fs≧2×Fc. The higher Fs is within the range allowed by the characteristics of each element of the magnetic detection device 10, the more it contributes to improving the detection accuracy. Fc is expressed as Fc≧Ft×K, where the rotational speed of the rotating body 20 is Ft [Hz] and the number of convex portions 21 or concave portions 22 per revolution of the rotating body 20 is K [pieces].

FIG. 8 is a circuit diagram of a magnetic detection device according to Comparative Example 1. The circuit of FIG. 8 is different from the first embodiment shown in FIG. 6 in that the input voltage to the GMR element bridge circuit is changed from the output voltage V _EXT of the signal generation section 18b to the power supply voltage Vcc. The difference is that a multiplier 18c is added between the output terminal of the differential amplifier 17 and the input terminal of the low-pass filter 18a, and that the output voltage V _EXT of the signal generation section 18b is also input to the multiplier 18c. , otherwise identical. The low-pass filter 18a, the signal generation section 18b, and the multiplier 18c constitute a synchronous detection section that synchronously detects the magnetic field signal applied to the GMR element bridge circuit.

Hereinafter, in each circuit of FIGS. 6 and 8, the resistance values of the GMR elements 15a and 15d are R _MR+ , the resistance values of the GMR elements 15b and 15c are R _MR- , the voltage of the inverting input terminal of the differential amplifier 17 is Va, The voltage of the non-inverting input terminal is Vb, the voltage of the output terminal of the differential amplifier 17 is Vdiff, the output voltage of the signal generation section 18b is V _EXT , the current flowing through the coil 12 is I _EXT , and the output voltage of the multiplier 18c is V _MULTI (FIG. 8 only), the output voltage of the low-pass filter 18a is set to Vout.

In the circuit of Embodiment 1 shown in FIG. 6, the multiplier 18c in the circuit of Comparative Example 1 shown in FIG. 8 is not present. However, the output voltage Vdiff of the differential amplifier 17 in the circuit of the _embodiment shown in _FIG . It becomes a voltage signal equivalent to (a voltage signal that has been multiplied in the process of synchronous detection). This is because the input voltage to the GMR element bridge circuit is set to the output voltage V _EXT of the signal generating section 18b. This point will be explained below.

If the resistance value of the GMR elements 15a to 15d in the absence of a magnetic field is R ₀ and the amount of change in resistance value due to the magnetic field is Δr, then
R _MR+ = R ₀ + Δr Formula 1
R _MR- = R ₀ - Δr Formula 2
It is expressed as Δr changes depending on the magnetic field H applied to the GMR elements 15a to 15d,
Δr=αH Equation 3
It is expressed as α is a constant determined by the rate of change in resistance of the GMR elements 15a to 15d. In addition, the magnetic field H is
H=βI _EXT formula 4
It is expressed as β is a coefficient determined by the configuration (number of turns, diameter) of the coil 12, the distance and positional relationship between the coil 12 and the GMR elements 15a to 15d, and the relative position of the rotating body 20 with respect to the magnetic detection device 10. β is an unchanging constant if the relative position of the rotating body 20 with respect to the magnetic detection device 10 is constant, but changes if the relative position changes (that is, if the rotating body 20 rotates). When the rotating body 20 is non-magnetic and conductive, β becomes small when the magnetic detection device 10 faces the convex portion 21 of the rotating body 20, and becomes large when the magnetic detection device 10 faces the concave portion 22. That is, when the rotating body 20 rotates, β changes at the variation frequency Fc [Hz] of the facing distance between the rotating body 20 and the magnetic detection device 10. From equations 3 and 4,
Δr=αβI _EXT formula 5
becomes.

となる。差動増幅器１７の出力電圧Ｖdiffは、
Ｖdiff＝Ａdiff（Ｖａ－Ｖｂ） 式８
と表される。Ａdiffは、差動増幅器１７のゲイン（定数）である。式６～式８より、

となる。乗算器１８ｃの出力電圧Ｖ_MULTIは、
Ｖ_MULTI＝Ｖdiff×Ｖ_EXT 式１０
で表される。式９より、

となる。さらに、式５より、

となる。 In the circuit of Comparative Example 1 shown in FIG. 8, the voltage Va at the inverting input terminal and the voltage Vb at the non-inverting input terminal of the differential amplifier 17 are as follows.

becomes. The output voltage Vdiff of the differential amplifier 17 is
Vdiff=Adiff(Va-Vb) Equation 8
It is expressed as Adiff is the gain (constant) of the differential amplifier 17. From equations 6 to 8,

becomes. The output voltage V _MULTI of the multiplier 18c is
V _MULTI = Vdiff×V _EXT formula 10
It is expressed as From equation 9,

becomes. Furthermore, from equation 5,

becomes.

となる。差動増幅器１７の出力電圧Ｖdiffは、式８、式１３、式１４より、

となる。さらに、式５より、

となる。 In the circuit of the first embodiment shown in FIG. 6, the voltage Va at the inverting input terminal and the voltage Vb at the non-inverting input terminal of the differential amplifier 17 are as follows.

becomes. From equations 8, 13, and 14, the output voltage Vdiff of the differential amplifier 17 is

becomes. Furthermore, from equation 5,

becomes.

In this way, the output voltage Vdiff (Equation 16) of the differential amplifier 17 in the circuit of the first embodiment shown _in FIG. ) is proportional to Therefore, in the circuit of the first embodiment shown in FIG. 6, the signal after passing the output voltage Vdiff of the differential amplifier 17 through the low-pass filter 18a (sensor output voltage Vout) is the magnetic field signal applied to the GMR element bridge circuit. The signal is the result of synchronous detection of That is, although the circuit of the first embodiment shown in FIG. 6 does not have the multiplier 18c unlike the first comparative example shown in FIG. 8, the multiplied signal is obtained as the output voltage Vdiff of the differential amplifier 17. Therefore, synchronous detection is possible without the multiplier 18c.

FIG. 7 is a simulated waveform diagram of the magnetic field H applied to the GMR element bridge circuit and the sensor output voltage Vout in the circuit of the first embodiment shown in FIG. FIG. 9 is a simulated waveform diagram of the magnetic field H applied to the GMR element bridge circuit and the sensor output voltage Vout in the circuit of Comparative Example 1 shown in FIG. From the comparison between FIGS. 7 and 9, the simulation results show that if the magnetic field H applied to the GMR element bridge circuit is the same, the sensor output voltage Vout of the circuit of the first embodiment shown in FIG. It was confirmed that the sensor output voltage Vout in the circuit of Comparative Example 1 shown in FIG.

According to the present embodiment, in order to supply the output voltage VEXT of the signal generation section 18b, which is a signal for generating an alternating magnetic field in the coil 12, to the GMR element bridge circuit as an operating voltage, the output voltage of the GMR element bridge circuit ( Va-Vb) becomes a multiplied signal (voltage proportional to IEXT×VEXT). Therefore, synchronous detection of the magnetic field signal applied to the GMR element bridge circuit is possible without providing a dedicated circuit for multiplication (for example, the multiplier 18c of the circuit of Comparative Example 1 shown in FIG. 8). Therefore, the moving object detection device 1 and the magnetic detection device 10 of this embodiment do not require a dedicated circuit for multiplication, so they are small and low in cost.

(Embodiment 2)
Embodiment 2 of the present invention will be described with reference to FIG. The moving object detection device 2 of this embodiment is different from that of the first embodiment in that the rotating body 20 is replaced with a rotating body 30, and is the same in other respects. The rotating body 30 has a disk shape or a regular polygonal plate shape, and has a high conductivity or high permeability part 31 as a first part and a low conductivity or high permeability part 31 as a second part on the outer peripheral surface (outer peripheral part). It has a low magnetic permeability portion 32. In the example of this embodiment, the high conductivity or high magnetic permeability portions 31 and the low conductivity or low magnetic permeability portions 32 are provided on the outer peripheral surface of the rotating body 30 alternately at the same pitch over the entire circumference. Examples of the structure of the rotating body 30 include a plastic gear in which the concave part is filled with metal plating such as copper or aluminum (the plastic part is a low conductivity part and the metal part is a high conductivity part), The concave part of a gear made of non-magnetic material such as aluminum is filled with soft magnetic material by plating with permalloy or printing with ferrite powder (the non-magnetic material part has low magnetic permeability, and the soft magnetic material part has high magnetic permeability). Can be mentioned.

The principle of rotation detection of the rotating body 30 in this embodiment is the same as that in the first embodiment. Specifically, when the high conductivity or high permeability portion 31 of the rotating body 30 faces the magnetic detection device 10, when the convex portion 21 of the rotating body 20 faces the magnetic detection device 10 in the first embodiment, corresponds to When the low conductivity or low magnetic permeability portion 32 of the rotating body 30 faces the magnetic detection device 10, this corresponds to when the recess 22 of the rotating body 20 faces the magnetic detection device 10 in the first embodiment. This embodiment can also produce the same effects as the first embodiment. Further, according to the present embodiment, the rotating body 30 may have a portion (body portion) other than the high conductivity or high permeability portion 31 made of a non-magnetic material such as plastic and an insulating material.

(Embodiment 3)
Embodiment 3 of the present invention will be described with reference to FIG. The moving body detection device 3 of this embodiment differs from that of the second embodiment in that the magnetic detection device 10 is located at a non-center portion of the rotor 40 on one side in the axial direction of the rotor 40, preferably at a portion near the outer peripheral edge ( It is provided at a position facing the outer peripheral part). The axial direction of the coil 12 is preferably parallel to the axial direction of the rotating body 40. Further, the rotary body 40 has a high conductivity or high permeability portion 41 as a first portion and a second portion on one surface in the axial direction at a position where it can face the magnetic detection device 10 due to its rotation. It has a low conductivity or low permeability portion 42 as shown in FIG. The high conductivity or high magnetic permeability portions 41 and the low conductivity or low magnetic permeability portions 42 are provided alternately over the entire circumference at the same pitch so as to go around the axis of the rotating body 40 . Note that the high conductivity or high magnetic permeability portion 41 is provided so as to protrude toward the magnetic detection device 10 side compared to the low conductivity or low magnetic permeability portion 42, but the low conductivity or low magnetic permeability portion It may be flush with 42. Other points of this embodiment are the same as those of the second embodiment. This embodiment can also produce the same effects as the second embodiment.

(Embodiment 4)
Embodiment 4 of the present invention will be described with reference to FIG. The moving object detection device 4 of the present embodiment differs from that of the first embodiment in that the magnetic detection device 10 is located at a non-center portion of the rotating body 50 on one side in the axial direction of the rotating body 50, preferably at a portion near the outer peripheral edge ( It is provided at a position facing the outer peripheral part). The axial direction of the coil 12 is preferably parallel to the axial direction of the rotating body 50. Further, the rotating body 50 has a convex portion 51 as a first portion and a recessed portion 52 as a second portion on one surface in the axial direction at a position where it can face the magnetic detection device 10 due to its rotation. . The convex portions 51 and the concave portions 52 are provided alternately over the entire circumference at the same pitch so as to go around the axis of the rotating body 50. Other points of this embodiment are the same as those of the first embodiment. This embodiment can also produce the same effects as the first embodiment.

(Embodiment 5)
Embodiment 5 of the present invention will be described with reference to FIG. The moving object detection device 5 of this embodiment differs from Embodiment 4 in that the recess 52 is replaced with a through hole 62 and the protrusion 51 is replaced with a boundary 61, and is the same in other respects. That is, the rotary body 60 has a through hole 62 as a second portion on one surface in the axial direction at a position where it can face the magnetic detection device 10 due to its rotation. The through holes 62 are provided at the same pitch all the way around the axis of the rotating body 60 . A boundary portion 61 between adjacent through holes 62 corresponds to a first portion. The principle of rotation detection of the rotating body 60 in this embodiment is the same as that in the first embodiment. Specifically, when the boundary portion 61 of the rotating body 60 faces the magnetic detection device 10, this corresponds to when the convex portion 21 of the rotating body 20 faces the magnetic detection device 10 in the first embodiment. When the through hole 62 of the rotating body 60 faces the magnetic detection device 10, this corresponds to when the recess 22 of the rotating body 20 faces the magnetic detection device 10 in the first embodiment. This embodiment can also produce the same effects as the fourth embodiment.

(Embodiment 6)
FIG. 14 is a schematic perspective view of a moving object detection device 6 according to Embodiment 6 of the present invention. The moving body detection device 6 of this embodiment is obtained by replacing the rotating body 30 of the second embodiment shown in FIG. 10 with a linear moving body 70, and the configuration of the magnetic detection device 10 is the same as that of the second embodiment. It is. The linear moving body 70 has a planar shape, and has a high conductivity or high permeability part 71 as a first part and a second part on a surface facing the magnetic detection device 10 (hereinafter also referred to as "opposing surface"). It has a low conductivity or low magnetic permeability portion 72 as a portion. In the example of this embodiment, the high conductivity or high magnetic permeability portions 71 and the low conductivity or low magnetic permeability portions 72 are arranged alternately along the moving direction of the linear moving body 70 on the opposing surface of the linear moving body 70. provided at the same pitch. Examples of the configuration of the linear moving body 70 include a flat plate made of plastic whose recesses are filled with metal plating such as copper or aluminum (the plastic part is a low conductivity part, and the metal part is a high conductivity part); The concave part of a flat plate made of non-magnetic material such as aluminum or aluminum is filled with soft magnetic material by plating with permalloy or printing with ferrite powder (the non-magnetic material part is the low magnetic permeability part, and the soft magnetic material part is the high magnetic permeability part). can be mentioned. Note that the high conductivity or high magnetic permeability portion 71 and the low conductivity or low magnetic permeability portion 72 may have an uneven relationship. The principle of detecting the movement of the linear moving body 70 in this embodiment is the same as the principle of detecting rotation in the second embodiment. This embodiment can also produce the same effects as the second embodiment.

(Embodiment 7)
FIG. 15 is a schematic perspective view of a moving object detection device 7 according to Embodiment 7 of the present invention. The moving body detection device 7 of this embodiment is obtained by replacing the rotating body 60 of the fifth embodiment shown in FIG. 13 with a linear moving body 80, and the configuration of the magnetic detection device 10 is the same as that of the fifth embodiment. It is. The linear moving body 80 has a through hole 82 as a second portion at a position where it can face the magnetic detection device 10 by moving itself. The through holes 82 are provided at the same pitch along the moving direction of the linear moving body 80. A boundary portion 81 between adjacent through holes 82 corresponds to a first portion. The principle of movement detection of the linear moving body 80 in this embodiment is the same as the principle of rotation detection in the fifth embodiment. This embodiment can also produce the same effects as the fifth embodiment. Note that the same effect can be achieved by providing a recess (non-through hole) facing the magnetic detection device 10 side instead of the through hole 82.

(Embodiment 8)
Fig. 16 is a circuit diagram of a magnetic detection device 10A according to embodiment 8 of the present invention. The following mainly describes the differences from the magnetic detection device 10 according to embodiment 1 shown in Fig. 6. The magnetic detection device 10A has a negative feedback coil 12a as a negative feedback magnetic field generating conductor between the output terminal of a differential amplifier 17 and the input terminal of a low-pass filter 18a. One end of the negative feedback coil 12a is connected to the output terminal of the differential amplifier 17. The other end of the negative feedback coil 12a is connected to the input terminal of the low-pass filter 18a.

The negative feedback coil 12a generates a negative feedback magnetic field that brings the magnetic sensor 13 into a magnetically balanced state when the output current of the differential amplifier 17 flows therethrough. The magnetic equilibrium state is a state in which the magnetosensitive direction component of the magnetic field at the positions of the GMR elements 15a to 15d is a predetermined value (for example, zero). In this embodiment, the resistor 19 is a current-voltage conversion means that converts the current flowing through the negative feedback coil 12a into a voltage, and is provided between the other end of the negative feedback coil 12a and the ground. The magnetic detection device 10A detects the magnetic field signal applied to the GMR element bridge circuit by using the current flowing through the negative feedback coil 12a (negative feedback current I _FB ) to bring the magnetic sensor 13 into a magnetically balanced state. . That is, in the magnetic detection device 10 of the first embodiment, the magnetic field signal detection method is a magnetic proportional type, whereas in the magnetic detection device 10A of the present embodiment, the magnetic field signal detection method is a magnetic equilibrium type.

In the magnetic detection device 10A, the negative feedback current _IFB has a one-to-one linear relationship with the product of the current _IEXT flowing through the coil 12 and the input voltage _VEXT to the GMR element bridge circuit,
_IFB = γ × _IEXT × _VEXT Equation 17
The following relationship holds. γ is a coefficient determined by the gain of the differential amplifier 17, the degree of magnetic coupling between the negative feedback coil 12a and the GMR element bridge circuit, and β in the above-mentioned formula 4. The input voltage Vdiff to the low-pass filter 18a is expressed by using the resistance value Rs of the resistor 19 as follows:
Vdiff = Rs x _IFB
= Rs × γ × I _EXT × V _EXT Equation 18
This is a value proportional to the above-mentioned formula 16 in the magnetic detection device 10 of the first embodiment.

FIG. 17 is a circuit diagram of a magnetic detection device according to Comparative Example 2. The circuit of FIG. 17 differs from the second embodiment shown in FIG. 16 in that the input voltage to the GMR element bridge circuit is changed from the output voltage V _EXT of the signal generating section 18b to the power supply voltage Vcc. The difference is that a multiplier 18c is added between the other end of the negative feedback coil 12a and the input terminal of the low-pass filter 18a, and that the output voltage V _EXT of the signal generator 18b is also input to the multiplier 18c. and agree in all other respects. The low-pass filter 18a, the signal generation section 18b, and the multiplier 18c constitute a synchronous detection section that synchronously detects the magnetic field signal applied to the GMR element bridge circuit.

In the magnetic detection device according to Comparative Example 2,
I _FB = γ × I _EXT × Vcc Equation 19
Vdiff=Rs×I _FB
= Rs × γ × I _EXT × Vcc Equation 20
V _MULTI = Vdiff×V _EXT
=Rs×γ×I _EXT ×Vcc×V _EXT Formula 21
It is.

According to the present embodiment, since the alternating voltage V _EXT outputted from the signal generating section 18b is supplied to the GMR element bridge circuit as an operating voltage, the output voltage Vdiff (Equation 18) of the differential amplifier 17 is as shown in FIG. It is proportional to the output voltage V _MULTI (Equation 21) of the multiplier 18c in the magnetic detection device of Comparative Example 2. Therefore, in the magnetic detection device 10A shown in FIG. 16, the signal (sensor output voltage Vout) obtained by passing the output voltage Vdiff of the differential amplifier 17 through the low-pass filter 18a synchronizes the magnetic field signal applied to the GMR element bridge circuit. This is the signal that is the result of detection. That is, although the detection circuit 1C shown in FIG. 16 does not have the multiplier 18c unlike the comparative example 2 shown in FIG. 17, a multiplied signal is obtained as the output voltage Vdiff of the differential amplifier 17. , synchronous detection is possible without the multiplier 18c. Therefore, the magnetic detection device 10A of this embodiment and the moving object detection device using the same do not require a dedicated circuit for multiplication, and thus are small and low-cost. In the second to seventh embodiments, the magnetic detection device 10 in FIG. 6 may be replaced with the magnetic detection device 10A in FIG. 16.

Although the present invention has been described above using the embodiments as examples, those skilled in the art will understand that various modifications can be made to each component and each processing process of the embodiments within the scope of the claims. By the way. Modifications will be discussed below.

In the embodiment, an example was explained in which the position of the magnetic detection device is fixed and the movable body (rotating body or linearly movable body) moves (rotates), but even if the movable body is fixed and the magnetic detection device moves, good. That is, the movement of the moving object is relative movement with respect to the magnetic detection device, and it does not matter whether the moving object's absolute position moves. The moving body in Embodiments 1 to 5 may be a linear moving body such as a rack.

In the embodiment, the facing distance between the magnetic detection device and the moving body, or the electrical conductivity or magnetic permeability of the portion of the moving body that faces the magnetic detection device 10 is set to two different levels as the moving body moves. Although a configuration has been described in which values are alternately taken, a configuration in which values of three or more levels are alternately taken is also possible. Furthermore, changes in each parameter may be continuous as the moving object moves. For example, in the case of a moving body having sinusoidal irregularities, the facing distance to the magnetic detection device changes continuously as the moving body moves.

In the embodiment, four GMR elements 15a to 15d are connected in a full-bridge manner, but two GMR elements may be connected in a half-bridge manner, or one GMR element 15 and a fixed resistor may be connected in a half-bridge manner. The magnetically sensitive element is not limited to a magnetoresistive element such as a GMR element, but may be another type of element such as a Hall element. Note that in the case of a Hall element, the sensor output necessary for detection can be obtained even if it is placed on the central axis of the coil 12.

In the embodiment, the soft magnetic material 16 is provided in order to increase the sensor output, but the soft magnetic material 16 may be omitted if a sensor output of the required magnitude can be obtained. At least one concave portion, convex portion, high conductivity or high magnetic permeability portion, or low conductivity or low magnetic permeability portion of the moving body is sufficient, and when a plurality of them are provided, the arrangement pitch may be different from each other. The magnetic field generating conductor is not limited to a coil, and may be, for example, a linear current path.

1 to 7 Moving object detection device 10 Magnetic detection device 11 Substrate, 12 Coil (magnetic field generation conductor), 12a Negative feedback coil (negative feedback magnetic field generation conductor), 13 Magnetic sensor, 14 Magnetic sensing element chip, 15a to 15d GMR element (magnetoresistive effect element), 16 soft magnetic material, 17 differential amplifier, 18a low-pass filter, 18b signal generation section (voltage application section), 18c multiplier, 19 resistance,
20 rotating body (moving body), 21 convex part (first part), 22 concave part (second part),
30 rotating body, 31 high conductivity or high magnetic permeability part (first part), 32 low conductivity or low magnetic permeability part (second part),
40 Rotating body, 41 High conductivity or high magnetic permeability part (first part), 42 Low conductivity or low magnetic permeability part (second part)
50 rotating body (moving body), 51 convex part (first part), 52 concave part (second part),
60 rotating body (moving body), 61 boundary part (first part), 62 through hole (second part),
70 linear moving body, 71 high conductivity or high magnetic permeability part (first part), 72 low conductivity or low magnetic permeability part (second part),
80 linear moving body, 81 boundary (first part), 82 through hole (second part)

Claims (5)

A magnetic detection device that detects magnetic field changes due to relative movement of a moving object,
a magnetic field generating conductor;
a voltage application unit that applies an alternating voltage to the magnetic field generating conductor to generate an alternating magnetic field for application to a moving body;
a magnetic sensor having a bridge circuit including at least one magnetoresistive element to which a magnetic field generated by the magnetic field generating conductor and which changes due to relative movement of the moving object is applied;
A magnetic detection device that applies an alternating voltage output from the voltage application section to the bridge circuit . The magnetic detection device according to claim 1, further comprising a low-pass filter that passes the output signal of the magnetic sensor. a differential amplifier into which the output voltage of the magnetic sensor is input;
a negative feedback magnetic field generating conductor that is supplied with current from the differential amplifier and generates a negative feedback magnetic field that brings the magnetic sensor into a magnetically balanced state;
3. The magnetic detection device according to claim 2, further comprising current-voltage converting means for converting the current supplied from the differential amplifier to the negative feedback magnetic field generating conductor into a voltage and outputting the voltage to the low-pass filter. a magnetic detection device;
A moving body that moves relative to the magnetic detection device,
The magnetic detection device includes:
a magnetic field generating conductor;
a voltage application unit that applies an alternating voltage to the magnetic field generating conductor to generate an alternating magnetic field to be applied to the moving object;
a magnetic sensor having a bridge circuit including at least one magnetoresistive element to which a magnetic field generated by the magnetic field generating conductor and which changes due to relative movement of the moving body is applied;
A moving object detection device that applies an alternating voltage output from the voltage application section to the bridge circuit . The magnetic detection device includes a low-pass filter that passes the output signal of the magnetic sensor,
The moving body has first and second portions having mutually different electrical conductivity or magnetic permeability, or at least one convex portion or concave portion,
The frequency of the alternating voltage outputted by the voltage application section is a frequency equal to or higher than the fluctuation frequency of the electrical conductivity or magnetic permeability of the portion of the moving body that faces the magnetic detection device, or the frequency of the variation between the moving body and the magnetic detection device. The moving object detection device according to claim 4, wherein the frequency is higher than the frequency of variation in the facing distance.

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